Signal peptide is a sequence peptide, which comprises, dominantly, short hydrophobic amino acids (approximately 3 to 60 amino acids) in protein molecules and instructs secretion (transportation of the protein to endoplasmic reticulum). Such a signal peptide is also referred to as a “signal sequence,” “localization signal,” “transport (transfer) signal,” etc.
As signal sequences of bifidobacteria, the signal sequences of secretory proteins, such as amylase of Bifidobacterium adolescentis, or Sec1, Sec2 and Sec3 of Bifidobacterium breve, have been reported, for example. In addition, the present inventors have proposed a signal sequence that can be applied to a plasmid for transformation of bifidobacteria (see, for example, Patent Documents 1 and 2).
Other than these, the genomic analysis of Bifidobacterium longum has also been reported (see, for example, Patent Document 3).
Moreover, there have been proposed: a method which comprises screening for an antibody gene expressed in cancer patient-derived B cells from a cancer antigen library derived from cultured cancer cells, so as to identify a more universal novel antibody gene against cancer antigens, without limitation of a source for collecting B cells (see, for example, Patent Document 4); a method of providing a gene library consisting of combinations of immunoglobulin light-chain variable region genes and heavy-chain variable region genes (see, for example, Patent Document 5); and a method of producing an antibody, which is capable of efficiently preparing a highly-versatile monoclonal antibody in a short time (see, for example, Patent Document 6), etc.